Alex Tabarrok thinks he has Matt Yglesias in some kind of contradiction. In one place, Yglesias is saying that a commitment to utilitarianism isn't the main reason to support redistributive taxation. In another place, he suggests that the welfare-enhancing nature of redistributive taxation gives us reason to support it. There's no contradiction between these two claims.
Probably the best thing to do here is to say something about the structure of common-sense moral theory, which is far richer than utilitarianism. People generally think that increasing the general welfare is a good thing, as utilitarians do. But they think lots of other things are good too. For example, not violating people's rights is a good thing, even if doing so would be neutral with respect to aggregate welfare. And maybe the goodness of having an egalitarian society, or maintaining a democratic political system, are considered good independent of their contributions to welfare. And maybe a bunch of things, like keeping promises, are right independent of any goods that might result. But the fact remains that increasing the aggregate happiness is one among many goods.
Lots of philosophers have theories according to which the general welfare is one among many good things. Rawls, for example, isn't a utilitarian, but he'll support an increase in the general happiness, assuming that it doesn't hurt the people at the bottom. Basically everyone (except a few Kantians and some a priori libertarians) thinks that increasing the general happiness is good. So, as Matt says, "there's little grounds for the belief that a commitment to utilitarianism is the main justification for redistributive taxation." At the same time, a lot of people will agree that greater welfare gives you a reason to redistribute. You get strong arguments for welfare-enhancing measures like redistributive taxation in most of the non-utilitarian theories you look at.
(There's also a couple other things to say about how Yglesias only said that redistribution was welfare-enhancing, not that that made it good. But I think the thing about how lots of non-utilitarians still like enhancing welfare is probably the least nitpicky point.)